蛛形綱（學名：Arachnida）又名蜘蛛綱，是節肢動物下的一個綱，包括了蜘蛛、蠍子、壁蝨、螨等。蜘蛛、蠍子等常被大眾誤解為昆蟲，雖然同屬節肢動物門，可是它們都獨立於昆蟲綱之外，屬於蛛形綱。蛛形綱動物的特徵是擁有八隻腳，书肺，体内受精，半變態。蛛形綱動物大多在陸地生活，大部分為肉食性。有一些蜘蛛和蠍子有毒，主要用作自衛及捕獵用途，但大部分的蛛形綱都是無毒的。
根據2011年的分類，現時蛛形綱（Arachnida Cuvier, 1812）有大约112,201左右的物種，當中化石種有†1,586，可作以下分類[3]：
- Order 1
- Order 1.1 盲蛛目 Opiliones Sundevall, 1833: (6,519 species, of which †35 species)11
- Order 1.2 蝎目 Scorpiones C.L. Koch, 1851: (2,068 species, of which †121 species)12
- 跑足亚纲 Dromopoda
- Order 2.1 避日目 Solifugae Sundevall, 1833: (1,116 species, of which †3 species)13
- Order 2.2 拟蝎目 Pseudoscorpiones de Geer, 1778: (3,494 species, of which †40 species)14
- Order 3 鬚腳目 Palpigradi Thorell, 1888: (83 species, of which †1 species)15
- Order 4 †古怖目 Phalangiotarbida Haase, 1890: (†31 species )16
- Order 5 节腹目 Ricinulei Thorell, 1876: (73 species, of which †15 species)17
- 寄蟎總目 Parasitiformes[4]
- Order 6.1 節腹蟎目 Opilioacarida Zakhvatkin, 1952: (37 species, of which †2 species)18
- Order 6.2 巨蟎目 Holothyrida Thon, 1905: (27 species)
- Order 6.3 真蜱目 Ixodida Leach, 1815: (896 species, of which †5 species) 19
- Order 6.4 革蟎目 Mesostigmata G. Canestrini, 1891: (11,424 species)
- 蟎形總目 Acariformes
- Order 7.1 恙螨目 Trombidiformes Reuter, 1909: (25,821 species, of which †24 species)20
- Order 7.2 疥蟎目 Sarcoptiformes Reuter, 1909 (16,412 species, of which †113 species)21
- Order 8
- Order 8.1 †角怖目 Trigonotarbida Petrunkevitch, 1949 (†65 species)22
- Order 8.2.1.1 †乌拉尔蛛目 Uraraneida Selden & Shear in Selden et al., 2008 (†3 species)23
- Order 8.2.1.2 蜘蛛目 Araneae Clerck, 1757: (43,579 species, of which †1,106 species)24
- Order 8.2.2.1 †聯足目 Haptopoda Pocock, 1911 (†1 species)25
- 无鞭目 Amblypygi
- 有鞭目 Thelyphonida
- 裂盾目 Schizomida
- ^ Dunlop, J.A. A trigonotarbid arachnid from the Upper Silurian of Shropshire (PDF). Palaeontology. September 1996, 39 (3): 605–614 [2008-10-12].
- ^ Andrew J. Wendruff; Loren E. Babcock; Christian S. Wirkner; Joanne Kluessendorf; Donald G. Mikulic. A Silurian ancestral scorpion with fossilised internal anatomy illustrating a pathway to arachnid terrestrialisation. Scientific Reports. 2020, 10: Article number 14. doi:10.1038/s41598-019-56010-z.
- ^ Zhang, Zhi-Qiang. Phylum Arthropoda von Siebold, 1848 (PDF). Zhang, Z.-Q. (编). Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness (PDF). Zootaxa (Magnolia Press). 2011: 123–128. ISBN 978-1-86977-850-7. ISSN 1175-5334 （英语）.
- ^ FRÉDÉRIC BEAULIEU, ASHLEY P.G. DOWLING, HANS KLOMPEN, GILBERTO J. DE MORAES & DAVID EVANS WALTER. Superorder Parasitiformes Reuter, 1909 (PDF). Zhang, Z.-Q. (编). Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness (PDF). Zootaxa (Magnolia Press). 2011: 123–128. ISBN 978-1-86977-850-7. ISSN 1175-5334 （英语）.
